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manual: disambiguate field expressions from method-call expressions.

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Graydon Hoare 2012-10-11 11:57:12 -07:00
parent d81196ce96
commit 06a17a7ce5
1 changed files with 19 additions and 13 deletions
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doc/rust.md
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@ -1178,7 +1178,7 @@ trait shape {
This defines a trait with two methods.
All values that have [implementations](#implementations) of this trait in scope can have their `draw` and `bounding_box` methods called,
using `value.bounding_box()` [syntax](#field-expressions).
using `value.bounding_box()` [syntax](#method-call-expressions).
Type parameters can be specified for a trait to make it generic.
These appear after the name, using the same syntax used in [generic
@ -1558,13 +1558,27 @@ let base = {x: 1, y: 2, z: 3};
{y: 0, z: 10, .. base};
~~~~
### Method-call expressions
~~~~~~~~{.ebnf .gram}
method_call_expr : expr '.' ident paren_expr_list ;
~~~~~~~~
A _method call_ consists of an expression followed by a single dot, an identifier, and a parenthesized expression-list.
Method calls are resolved to methods on specific traits,
either statically dispatching to a method if the exact `self`-type of the left-hand-side is known,
or dynamically dispatching if the left-hand-side expression is an indirect [trait type](#trait-types).
### Field expressions
~~~~~~~~{.ebnf .gram}
field_expr : expr '.' expr
field_expr : expr '.' ident
~~~~~~~~
A dot can be used to access a field in a record.
A _field expression_ consists of an expression followed by a single dot and an identifier,
when not immediately followed by a parenthesized expression-list (the latter is a [method call expression](#method-call-expressions)).
A field expression denotes a field of a [structure](#structure-types) or [record](#record-types).
~~~~~~~~ {.field}
myrecord.myfield;
@ -1574,17 +1588,9 @@ myrecord.myfield;
A field access on a record is an [lvalue](#lvalues-rvalues-and-temporaries) referring to the value of that field.
When the field is mutable, it can be [assigned](#assignment-expressions) to.
When the type of the expression to the left of the dot is a boxed
record, it is automatically derferenced to make the field access
possible.
When the type of the expression to the left of the dot is a pointer to a record or structure,
it is automatically derferenced to make the field access possible.
Field access syntax is overloaded for [trait method](#traits)
access. When no matching field is found, or the expression to the left
of the dot is not a (boxed) record, an
[implementation](#implementations) that matches this type and the
given method name is looked up instead, and the result of the
expression is this method, with its _self_ argument bound to the
expression on the left of the dot.
### Vector expressions